Double or nothing!

Automakers will have to double their fleet-wide average fuel economy by 2025 if proposed federal rules take effect. Here’s how they’ll do it.

By Jim Gorzelany

CTW Features

The White House and major automakers recently signed off on a plan to boost automakers’ corporate average fuel economy to 54.5 mpg by 2025. How will what amounts to nearly a 100 percent increase in the nation’s fleet of new cars be possible?

Certainly, increased sales of all-electric and plug-in hybrid vehicles in the coming years will go a long way toward helping automakers meet this goal. But analysts agree the conventional internal-combustion engine will remain the primary source of propulsion for vehicles in the U.S. for some time to come.

“Gasoline engines will still power 80 to 90 percent of vehicles all the way through 2025,” predicts George Peterson, president of AutoPacific Group, a Tustin, Calif.-based automotive research firm.

Here’s a look at what automakers will employ and combine to help boost their models’ fuel economy down the road.

Weight Reduction.. Experts say that all else being equal, decreasing a vehicle’s weight by 10 percent enables about a three percent increase in fuel economy. Since not all motorists will find it practical or desirable to drive smaller cars, expect tomorrow’s fleet to still come in assorted shapes and sizes, but with extensive use of lighter-weight materials such as aluminum and carbon fiber instead of steel.

Slicker Aerodynamics. At highway speeds, more than half of an engine’s power goes to overcoming drag, which is also known as wind resistance. Cars that are designed with a lower so-called coefficient of drag allow the air to move around them more efficiently, meaning their engines require less power to reach and maintain higher speeds.

Variable-Cylinder Management. A few V8- and V6-powered vehicles are already able to seamlessly depower half of their engines’ cylinders at cruising speeds to realize as much as a 10 percent boost in fuel economy. Variable cylinder management should eventually find its way into even some of the smallest engines.

Automatic Stop-Start. This function automatically shuts down a vehicle’s engine during deceleration and while stopped to preserve fuel. It starts the engine up again immediately once the driver lifts off on the brake pedal. First used in hybrid-powered vehicles, this stop-start technology will be included in next-generation mainstream models from several manufacturers.

Mild Electrification. Adding a small electric motor to a conventional gasoline engine boosts both its power and its fuel economy. General Motors is rolling out “eAssist” models from Buick and Chevrolet in which a lithium-ion battery runs the motor and recharges itself from power recovered through braking. The aforementioned start-stop function further adds to the car’s frugality.

Advanced Transmissions. Expect to see gearboxes with as many as eight or more speeds as a fuel-saving measure. Alternatively, we’ll see wider availability of lighter-weight Continuously Variable Transmissions that eschew conventional gears for a belt and a set of pulleys.

Electric Power Steering. Now becoming widespread, this supplants the belt driven power steering system with a sophisticated, electrically operated version; this affords less drag on an engine to boost fuel economy slightly.